Infusion apparatuses, e.g., pumps, for automatically performing infusion by using syringes are conventionally known. A medicinal solution in a medicine bottle is drawn into the syringe through a needle. Alternatively, a medicine cartridge is stored in the syringe. After the syringe containing the medicinal solution is mounted on the pump, a syringe plunger is pushed by a slider of the pump at a constant rate, so that the infusion solution is automatically administered to the patient. Infusion apparatuses of this type are disclosed in JP-A-48-62289, JP-U-57-76637, and JP-B-63-443390.
In such an infusion apparatus, a medicinal solution or blood must be reliably injected at a predetermined flow rate to the patient without an abnormality. Thus, in the conventional infusion apparatus, a slider for pushing the plunger is controlled by using, e.g., a microcomputer system. In another conventional infusion apparatus, the supremum pressure at the needle is determined immediately before the medicinal solution is injected to the patient. The force to the plunger is then expected and calculated at the supremum. An alarm is produced or the operation of the pump is stopped when this supremum force is detected.
syringes used in the infusion apparatus are manufactured by various manufacturers. Their sizes or configurations are standardized to a certain degree. However, the syringes of different manufacturers have different inherent slidable or dynamic frictional resistance values. Accordingly, it needs various specification data, e.g., the slidable frictional resistance, stroke, and capacity of the syringes. The various specification data therefore can be stored by using an EPROM or the like. When data on the slidable frictional resistance of the syringe of a certain manufacturer is stored in the EPROM of one infusion apparatus, its apparatus adapts to that of the syringes according to the specifications of the manufacturer.
In the conventional infusion apparatus, however, even when the force to the plunger exceeds the supremum force to produce the alarm, sometimes no abnormality occurs. This is because injecting pressure changes are not considered, which depend on the viscosity of the medicinal solution, the needle gauge or size, and the injecting location (vein, artery or muscle) of the patient. More specifically, since the supremum force is set according to a medicinal solution having a low viscosity, it does not correspond to a high-calorie medicinal solution having a high viscosity that attracts attention lately. Also, the supremum force does not correspond to a reaction against the injecting pressure when a needle having a small gauge and thus a large pressure loss is used, and when injection into an artery is performed, which are influenced by the blood pressure. In a worst case, when the patient takes a sudden turn for the worse and the blood pressure is increased, infusion is sometimes stopped by an alarm.
Also, in the conventional infusion apparatus, an alarm is sometimes produced before the force to the plunger reaches a predetermined supremum, and the operating pump is stopped. This is because the friction factor between the barrel and the plunger is not considered. More specifically, to determine the net injection amount of the infusion solution from the force to the plunger, it is indispensable to consider the friction factor between the barrel and the plunger slidably mounted thereto.
Furthermore, since the conventional infusion apparatus employs a small capacity EPROM, it cannot store all the specification data of the syringes of different manufacturers and all the operation programs for use in these syringes. Therefore, different standard EPROMs for different manufacturers must be used. Hence, a label must be adhered to the infusion apparatus to indicate that this apparatus corresponds to the syringe of a specific manufacturer, thereby clarifying the syringe of which manufacturer can be used in this infusion apparatus. If a syringe of a manufacturer to which the infusion apparatus does not correspond is erroneously used, problems occur because the specification data of the syringe is different. Then, a medicinal solution cannot be supplied at a preset flow rate. Various types of alarm units provided for safety infusion operation are malfunctioned.
The present invention, made in view of the above situations, has as its object to provide an infusion apparatus for obtaining a net pressure for infusion from the force to a plunger by considering the friction factor between the syringe barrel and the plunger.
It is another object of the present invention to provide an infusion apparatus capable of switching the alarm level of the injection pressure over a plurality of levels by considering reactions caused by the viscosity of the medicinal solution, the gauge of the needle, and the injecting location (vein, artery or muscle) of the patient.
It is still another object of the present invention to provide a highly reliable, simple infusion apparatus which can reliably correspond to syringes, and inject a medicinal solution at a preset flow rate to the patient even when these syringes having various specifications are used.
An infusion apparatus according to the present invention comprises a syringe for storing a medicinal solution, driving means for pushing a plunger in the syringe barrel at a predetermined speed, a pressure sensor for detecting a force to the plunger, a comparator capable of receiving an output from the pressure sensor, supremum and lowest limit constant tables each connected to inputs of the comparator, and a selection switch for selecting supremum and lowest limit values output from the supremum and lowest limit constant tables. A signal from the pressure sensor or an analog signal is A/D converted into, e.g., an 8-bit digital signal by a pressure converter.
According to another embodiment, an apparatus may further comprise a learning function of updating the supremum and lowest limit values corresponding to an alarm produced within a predetermined period after infusion is started.
An infusion apparatus according to another embodiment comprises a syringe for storing a medicinal solution, driving means for pushing a plunger into the syringe barrel at a predetermined speed, a pressure sensor for detecting a force to the plunger, a pressure converter connected to a signal output from the pressure sensor, a pressure loss constant table for outputting a pressure loss based on a friction factor between the barrel and the plunger, and a subtracter for subtracting the pressure loss from a detected force output from the pressure converter to obtain a net pressure.
According to still another embodiment, an apparatus may further comprise a learning function of storing, as the pressure loss, a force obtained when the plunger in the empty syringe is pushed at the predetermined speed, in the pressure loss constant table in a RAM. The friction factor is determined based on the standards and manufacturer specifications of the syringe. Accordingly, various values are stored in the ROM.
An infusion apparatus according to this still another embodiment of the present invention, in which a movable slider is abutted on a syringe plunger, and the plunger is pushed by moving the slider, comprises driving means for pushing the slider at a predetermined speed, means for detecting a force to the plunger, syringe diameter means for detecting a capacity of the syringe, data storage means for storing specification data for various syringes, program storage means for storing operation programs for said various syringes, comparing means for comparing information output from the pressure sensor and the syringe diameter means, with the specification data of the syringes stored in the storage means to determine a specific syringe to be mounted, and switching means for selecting a predetermined operation program for said specific syringe among the operation programs stored in the program storage means according to a comparison result of the comparing means.